Analog focal plane arrays (FPAs) have a fixed well depth determined by the maximum capacitor size that can fit within each pixel. The capacitor integrates as much charge as is allowable and then the signal from each row or column of adjacent pixels is digitized in an ADC. This leads to image saturation and does not allow quality images of scenes having a wide dynamic range (e.g., dim objects and bright objects). In the analog approach, the true signal generally cannot be recovered after the image saturates.
One approach to generating high dynamic range (HDR) images is to acquire data at different exposures, integration times, or gains, and then stitch these images together depending on the signal present in the scene. Other techniques employ a logarithmic response function at the pixel level. Using these techniques, high dynamic range scenes can be sufficiently displayed for human visual consumption. However, there are shortfalls associated with conventional HDR techniques, including: (1) image acquisition periods that are long enough to be susceptible to scene motion; (2) information loss due to gaps in the transfer function (of counts to photons), low signal-to-noise ratio (SNR), or both; and (3) complicated processing to piece together the HDR image from many images with low dynamic range. Achieving full rate video HDR can also be challenging.